1. Field of Invention
This invention relates to security tags and, more particularly, to an ultra-high frequency (UHF) dipole antenna system for a radio frequency identification (RFID) tag that optimizes detection for a given available volume in which to situate the RFID tag.
2. Description of Related Art
Low cost tags manufactured by continuous feed processes are normally formed from tag stock and are therefore two-dimensional. The performance of two-dimensional tags is generally a strong function of the orientation of the tag's antenna relative to the antenna of the tag interrogator and reader.
One approach used for reducing the sensitivity of tags to their orientation with respect to the interrogator/reader include increasing the effective area of the tag antenna so that greater energy is extracted from the incident electromagnetic field. Another approach, used with dipole antennas, is to orient two or more antennas at angles to each other within the plane of the tag stock. However, both of the aforementioned approaches results in a larger tag, adding manufacturing expense and reducing marketability.
To accommodate the use of two dipole antennae in RFID tags, one company, Matrics, Inc. of Rockville, Md., has developed an RFID system IC (e.g., on Matrics Tag X1020) that provides for a plurality of RF inputs along with a ground terminal.
However, especially where UHF frequencies (e.g., 850 MHz–950 MHz) and microwave frequencies (e.g., 2.3 Ghz–2.6 Ghz) are used in communicating with RFID tags, there remains a need for a UHF(or microwave) dipole antenna system that optimizes detection for a given volume in which the RFID tag is positioned.
All references cited herein are incorporated herein by reference in their entireties.